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Matthew Smith, a data journalist at the polling firm, said: "In Scotland, the notion of the 'True Scotsman' has long applied to one who does not wear anything beneath his kilt.

"Nevertheless, Scottish sports stars like Andy Murray have admitted to wearing underwear beneath their kilts - indeed Highland dancers and athletes are obliged by the rules of their various games to compete with underwear beneath their kilts."

The firm's research found that overall a total of two thirds of Scotsmen said they had worn a kilt at one time or another, rising to three quarters for those born in Scotland.

Of those who have worn a kilt, 55 per cent said they tend to wear underwear, while 38 per cent go without. Another seven per cent wear shorts, tights or something else, Mr Smith said.

He said: "Those who support Scottish independence are clearly a hardier sort, and are more likely to wear nothing underneath their kilts."

In 2010, The Scottish Tartans Authority sparked debate when it decreed that refusing to put on underwear beneath a kilt was "childish and unhygienic" and flew in the face of decency.

Brian Wilton, then director, said kilt wearers should have the "common sense" to realise sartorial times had moved on.

He said: "People should not be browbeaten into believing that nonsense. Just because Highlanders wore nothing in the days before Y-fronts were invented doesn't mean that we, in the 21st Century, should wear nothing too."

The YouGov research conducted in late September found more than nine-out-of-10 Scottish women said a kilt was an attractive look for a man. Two-fifths said nothing should be worn underneath and the same proportion said underwear was necessary. The rest did not know